Sunday, 17 February 2013

Woodcock on the wane


A long wander through my local Wormley Woods coincided with the arrival of the latest BTO newsletter. Woodcock was the connecting factor.  I saw 2 Woodcock; one flushed by me and one by a dog.  Wormley Woods are very popular with dog walkers and cyclists. Even the remote corner I explored had an off-the-leash labrador tearing through it. I doubt I could find any significant area of the wood without a squidgy tyre print or a doggy do.  I later flicked through the BTO newsletter and settled on the feature on the forthcoming Woodcock survey before shifting to the BTO website.  Woodcock have declined significantly in recent decades. The old CBC recorded a 74% decline between 1968 and 1999.  A quick look at the recent Atlas results appear to show that Woodcock in Hertfordshire in particular have dropped away sharply between the last two atlases, with the Broxbourne Woods complex remaining a very small and tenuous toehold in the county.  No-one really knows why they are declining but, low and behold, recreational disturbance, the drying out of woodland, overgrazing by deer and declining woodland management have been put forward as possible causes.  All four could apply to Wormley Woods.  No doubt the Woodland Trust and Natural England are actively considering these issues at this very moment.

It is undoubtedly good that people get out and enjoy wildlife-rich areas, including nature reserves, as human indifference to wildlife is arguably its greatest threat.  Yet disturbance to the very wildlife that we are encouraging people to visit and enjoy is a real issue that can be subtle in its effects.   Research has shown that disturbance can affect settling rates and patterns of breeding birds, lower their productivity, and can result in reduced densities and delayed breeding.

Studies of Nightjar (formerly present in the local woods but now gone) have found a reduction in breeding densities on sites heavily used by people and dogs.  Increased nest failure due to daytime egg predation was found to be the cause, particularly where nests are close to paths.  The theory goes that as sitting birds are flushed from nests, the eggs are exposed to predation, with the main predator suspected to be crows.

The distribution of Woodlarks on Dorset heaths was also found to be significantly affected by the presence of people and dogs.  Within sites with recreational access, the probability of suitable habitat being colonized was lower in those areas with greater disturbance; this was reduced to below 50% at around eight disturbance events per hour. However, there was no effect of disturbance on daily nest survival rates.  Birds on sites with higher levels of disturbance fledged more chicks (per pair) owing to a strong density-dependent increase in reproductive output.  However, in the absence of disturbance, overall productivity would be 34% higher.

Further afield, a fascinating study on the island of Ouessant in France showed that visitors had a detrimental impact on the survival of juvenile Chough simply by scaring them away from feeding sites.  Annual survival rates of juveniles were found to be negatively correlated with the number of visitors during August.  The time spent foraging by juveniles was 50% less than expected during this peak tourist month.  Food for thought.  Or not, if it happens to be August.

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